1. Field of the Invention
The present invention relates to a method and system for displaying flickerless X-ray dynamic images in TV camera photography simultaneously performed with cinecamera photography.
2. Description of the Related Art
A conventional apparatus for simultaneously photographing an X-ray image of an object by both a cinecamera and a TV camera is used in circulatory organ diagnosis systems and the like. The number of fields used in TV-camera photography is standardized at 60 fields/sec (the numbers of odd and even field periods). However, the number of fields in cinecamera photography can be arbitrarily determined; current trend has shifted this number from 60 fields/sec to 30 fields/sec. For example, when the number of fields in the cinecamera photography is the same as that in the TV-camera photography, i.e., 60 fields/sec, one X-ray radiation (synchronized with the cinecamera) is performed during one field period without synchronizing the photography timing of the cinecamera with that of the TV camera. Therefore, the brightness levels of the odd and even field periods included in one frame of a video signal are identical, thus displaying excellent X-ray images on a TV monitor.
On the other hand when the number of field in the cinecamera is set at 30 fields/sec, since only one X-ray is radiated during one frame, a video signal including two field periods (the odd and even field periods) each having the same brightness level cannot be obtained. For example, as shown in FIG. 1, the video signal having a high brightness level is detected during first one field period Tf. However, during the next one field period Tf', since interlaced scanning is performed between scanning lines scanned in first period Tf, the video signal having a low brightness level is detected. More specifically, since the video signal detected in accordance with the scanning in first period Tf includes the video signal detected in accordance with the scanning in next field period Tf', the video signal having the low brightness level is detected in the scanning in next field period Tf'. Therefore, a difference between brightness levels occurs, thereby causing flickering of the X-ray images displayed on the TV monitor.
In order to eliminate the above disadvantage, as shown in FIG. 2, an X-ray cinecamera apparatus for operating the cinecamera in synchronism with a TV synchronous signal and displaying the X-ray images in accordance with pseudo interlaced scanning is used. Referring to FIG. 2, X-ray tube 1 radiates an X-ray to subject 2. The X-ray received through subject 2 is converted into light by image intensifier (I.I) 3; this light is incident on optical system 4. The X-ray image of subject 2 is formed by the light incident on optical system 4. The formed X-ray image is photographed by TV camera 5 and cinecamera 6. Note that TV camera 5 includes a camera control unit (not shown) for controlling the TV camera 5.
A video signal output from TV camera 5 is input to sync-separator 10 in system processor 19. Syncseparator 10 separates TV synchronous signal S from the input video signal, as shown in FIG. 3A. TV synchronous signal S includes vertical synchronous signal S.sub.V which separates one frame from the next. Each frame consists of an odd field period (represented by "o") and an even field period (represented by "e"). The video signal output from the TV camera 5 s converted into a digital signal by A/D converter 12 and stored in field memory 13. The video signal read out from field memory 13 is converted into an analog signal by D/A converter 14 and output to TV monitor 16.
Vertical synchronous signal S.sub.V separated by syncseparator 10 is input to timing controller 15. Timing controller 15 comprises, e.g., a pulse generator, and the like, and it controls timings for writing and reading the video signal with respect to field memory 13. Vertical synchronous signal S.sub.V separated by syncseparator 10 is also input to pulse generator 11. Pulse generator 11 outputs cinecamera synchronous signal a synchronized with vertical synchronous signal S.sub.V to cinecamera controller 8 (FIG. 3B). Cinecamera controller 8 controls the timing of X-ray radiation from X-ray tube 1 and an operation of cinecamera 6. Note that X-ray tube 1 is controlled by X-ray controller 9.
Cinecamera synchronous signal a is generated by pulse generator 11 every from in synchronism with vertical synchronous signal S.sub.V separated by syncseparator 10, and is input to cinecamera controller 8. Cinecamera controller 8 generates cinecamera shutter pulse signal b in response to cinecamera synchronous signal a (FIG. 3C) and outputs signal b to X-ray controller 9 and cinecamera 6. X-ray controller 9 generates X-ray pulse signal c at this timing (FIG. 3D) and outputs signal c to X-ray tube 1. Therefore, X-ray tube 1 radiates X-ray to subject 2. Note that since the number of frames in photography of cinecamera 6 is set at 30 frames/sec, X-ray tube 1 radiates the x-ray every 1/30 sec.
When the X-ray is radiated from X-ray tube 1, TV camera 5 with the same timing as above scans for the odd field period for 1/60 sec and outputs video signal d having a waveform such as "o1" for 1/60 sec (FIG. 3E). Then, scanning of the even field period is performed. In this case, since the X-ray is not radiated from X-ray tube 1, TV camera 5 outputs video signal d having a waveform such as "e1" for 1/60 sec (FIG. 3E). Only video signal d, having a waveform such as "o1" output from TV camera 5, is written into field memory 13 in response to memory write signal e with the same timing as vertical synchronous sigal S.sub.V, i.e., for 1/60 sec (FIG. 3F).
Video signal d, written into field memory 13, is continuously read out therefrom in response to memory output signal f during the next even and odd field periods (FIG. 3G). One-frame video signal g is input to TV monitor 16 during these even and odd field periods (FIG. 3H). Therefore, since the video signal is output during one frame including the odd and even field periods, pseudo interlaced scanning is performed, thereby displaying flickerless X-ray images on TV monitor 16.
As described above, since the conventional X-ray cinecamera apparatus must operate the cinecamera in synchronism with the TV synchronous signal, the syncronization system is complicated and the apparatus is expensive.
As has been described above, the apparatus for displaying flickerless X-ray images without the synchronization system of the TV camera and the cinecamera has been desired.